This invention relates to swept frequency oscillator arrangements in which the output frequency can be varied in a controlled manner so as to sweep over a predetermined frequency range. A number of applications require the use of a swept frequency oscillator arrangement, and one such requirement exists in a spectrum analyser which is used to indicate the presence of particular frequencies in a received wide band electrical signal. The output frequency of a variable frequency oscillator is not always linearly related to the level of the control signal fed to it and which is used to change its frequency; that is to say, the tuning sensitivity of the oscillator is not constant, but is a function of the frequency at which it is oscillating. Because of this it has been customary to provide a degree of pre-distortion for the control signal to compensate for known non-linearities in the oscillator characteristics and this has been achieved by using a transistor or diode shaper network whose gain is a function of its input signal level. Networks of this kind use a large number of circuit components, can be extremely difficult to set up accurately, and have limited versatility. The present invention seeks to provide an improved swept frequency oscillator arrangement.